1. Field of the Invention
The present invention relates to a light source lamp that supplies illuminating light to an endoscope, and a battery-powered light source device for an endoscope equipped with a battery, which supplies power to this light source lamp.
2. Description of the Related Art
Endoscopes have come to be used in a wide range of fields today, both in medicine and industry. What these endoscopes are used to examine are the inside of the body or the inside of factory machinery or the like, and therefore some means is necessary for illuminating the site to be examined. Accordingly, with a standard endoscope, a light source device is readied as an external part of the endoscope, and illuminating light is guided from a light source lamp attached to the light source component in this light source device into a light-guide fiber provided to the endoscope, the illuminating light guided by this light-guide fiber is emitted from an illumination window at the tip of the insertion component, and the site to be examined is illuminated.
The above-mentioned light source device utilizes power supplied from a commercial power supply to light a power supply lamp inside the light source device.
Some endoscopes have a battery-powered light source device that makes use of a dry cell or other such battery as its power supply and is removably attached to the controls of the endoscope. An endoscope such as this is easier to carry around and can be used in places where there is no electrical outlet, which makes it suited to use outdoors or in emergency situations.
Nevertheless, the above-mentioned battery-powered light source devices used for endoscopes are connected to a separate auxiliary power supply unit and the voltage that is supplied to the light source lamp is boosted in order to make the light source lamp brighter. Here, because the above-mentioned battery-powered light source device has to be connected to an external power supply, the connection of the auxiliary power supply unit is troublesome. Also, because the voltage is boosted in stages when the auxiliary power supply unit is used with the above-mentioned battery-powered light source device for an endoscope, it is difficult to supply the proper voltage to the light source lamp.
When a conventional battery-powered light source device for an endoscope such as this is switched on, electrical power from the battery lights the illuminating lamp. The illuminating light from the illuminating lamp is guided to the input end of a light guide that is inserted through the inside of the endoscope from the control of the endoscope, and the site to be examined is illuminated from the tip of the endoscope insertion component.
There are times when a brighter lamp is desired so that the illuminating light will reach the site being examined, such as when the site is far away from the tip of the endoscope insertion component. In such cases, the illuminating lamp is made to shine more brightly by increasing the number of batteries and electrically connecting them in series.
However, a battery-powered light source device in which the illuminating lamp is made to shine more brightly by increasing the number of batteries as above becomes larger and heavier, which makes it more difficult to attach to and detach from the endoscope control.
Another problem with a battery-powered light source device is that when the battery voltages drops as the battery is used, the input current has to be increased in order to keep the voltage of the output consistent. Consequently, the power supply circuit is subjected to stress in a conventional battery-powered light source device. In view of this, a method has been adopted in which the current is monitored and a field effect transistor (FET) is used to switch off the device to protect it, as is commonly done with the protection circuits of lithium ion cells.
However, with a protection circuit in which the current is monitored and an FET is used to switch off the device, there is greater loss in the resistors used for monitoring the current, the high ON resistors of the FET, and so on, which is a problem in that the energy of the battery cannot be used as efficiently.
Also, in the supply [of voltage] to the lamp with a battery-powered light source device such as this, the battery voltage was boosted before being supplied to the lamp so that the lamp would shine more brightly. This step-up circuit was designed to keep the output voltage at a consistent level.
In this case, with a light source device that used a battery, the battery needed to be protected against overdischarging and short-circuiting, so the circuit had to provide a short-circuiting protection function and also had to reliably inform the user when the battery ran low, so as to prevent overdischarging.
In view of this, in Japanese Patent Application 2000-22405, which has already been submitted by the present applicant, the user was apprised of a low battery state by the provision of a second output state in which the output of the DC/DC [converter] was not as bright as usual, but the problem was that if the user kept on using the device, the terminal voltage would be exceeded and overdischarging would result.
Also disclosed was a means for flashing a lamp using an FET and thereby notifying the user, but the problem was that if the power applied to the lamp fluctuated, then the power of the control means would fluctuate at the same time, and another problem was that an extremely large surge current flowed when the lamp was turned on and off and when the power was turned on. Accordingly, a DC/DC [converter] was generally provided both for the load and for the control means, and it was difficult to share a power supply between the load and the control means with a single DC/DC converter, and thereby protect the batter and control the load.